Sleep disordered breathing describes a group of disorders such as snoring and obstructive sleep apnea and is characterized by abnormalities of respiratory pattern or the quantity of ventilation during sleep. Obstructive sleep apnea (OSA), the most common such disorder, is characterized by the repetitive collapse or partial collapse of the pharyngeal airway during sleep and the need to arouse to resume ventilation. Sleep is thus disrupted, yielding waking somnolence and diminished neurocognitive performance. The recurrent sleep arousal in association with intermittent hypoxia and hypercapnia has been implicated in the occurrence of adverse cardiovascular outcomes. In addition, there is evolving evidence that obstructive sleep apnea may contribute to insulin resistance and other components of the metabolic syndrome. Despite considerable progress, most patients remain undiagnosed and the principal therapeutic approach, continuous positive airway pressure (CPAP), remains somewhat cumbersome and hence not associated with optimal compliance rates.
Obstructive sleep apnea is caused by a blockage of the airway, which usually occurs when the soft tissue in the throat collapses and closes during sleep. FIG. 1 shows a cross-section of the naso-pharyngeal N area of a human. The mouth M and tongue T are shown along with a hard palate HP that separates the oral cavity from the nasal cavity. The soft palate SP extends from the hard palate HP and terminates by forming a uvula UV. Below the soft palate SP, the pharyngeal wall PW defines the throat passage TP. Below the epiglottis EP, the throat passage TP divides into a trachea TR for passing air to the lungs and an esophagus ES for passing food and drink to the stomach. The epiglottis EP closes the trachea TR during swallowing and drinking and opens for breathing.
During each apnea event, the brain briefly arouses the sufferer in order to initiate the resumption of breathing, however, this type of sleep is extremely fragmented and of poor quality. When left untreated, sleep apnea may result in high blood pressure, cardiovascular disease, weight gain, impotency, headaches, memory problems, job impairment, and motor vehicle crashes.
According to the National Institutes of Health, OSA is rather common and affects more than twelve million Americans. OSA affects males more than females. Other risk factors include being overweight and over the age of forty. Sleep apnea, however, can strike anyone at any age, even children. Despite the seriousness of OSA, a lack of awareness by the public and healthcare professionals results in the vast majority of patients remaining undiagnosed and untreated.
Continuous positive airway pressure (CPAP), which delivers air into the airway through a specially designed nasal mask or pillow, has been adopted as a treatment for obstructive sleep apnea. The flow of air creates positive pressure when the patient inhales to keep the airway open. CPAP is considered by many to be the most effective non-surgical treatment for the alleviation of snoring and obstructive sleep apnea, however, patients complain about discomfort from the mask and hoses, including bloating, nasal drying, and dry eyes. As a result, patient compliance is only about 40 percent.
Surgical treatments have also been employed. One such treatment is referred to as uvulopalatopharyngoplasty (UPPP), which involves removing about 2 cm of the trailing edge of the soft palate to reduce the soft palate's ability to flutter between the tongue and the pharyngeal wall of the throat. The procedure has been effective in alleviating snoring, but is painful and frequently results in undesirable side effects. In particular, removal of the trailing edge of the soft palate compromises the soft palate's ability to seal off nasal passages during swallowing and speech. As a result, in 25 percent of patients receiving UPPP, fluid escapes from the mouth and flows into the nose while drinking.
Another surgical procedure uses a laser to create scar tissue on the surface of the soft palate. The scar tissue reduces the flexibility of the soft palate, which, in turn, reduces snoring and/or closing of the air passage. Cautery-assisted palatal shaping operation (CAPSO) is a recently developed office-based procedure performed with local anesthesia. A midline strip of soft palate mucosa is removed, and the wound is allowed to heal. The flaccid palate is stiffened, and palatal snoring ceases.
Other surgical approaches have been tried that employ the use of RF or microwave energy (Somnoplasty) to shrink tissue in the tongue or soft palate. Radiofrequency ablation of the soft palate is used to produce thermal lesions within the tissues. Somnoplasty devices have been approved by the U.S. Food and Drug Administration (FDA) for radiofrequency ablation of palatal tissues for simple snoring and for the base of the tongue for OSA. In some situations, radiofrequency of the soft palate and base of tongue are performed together as a multilevel procedure. To date, the treatments alone or in combination have failed to provide relief to more than 50 percent of patients suffering from obstructive sleep apnea.
Another device intended to treat snoring or obstructive sleep apnea uses several braided PET cylinders that are implanted to make the tissues of the tongue or uvula more rigid and less prone to deflection against the pharyngeal wall. The Pillar™ Palatal Implant System sold by Restore Medical of St. Paul, Minn., is an implantable device that has been cleared by the FDA. The device is a cylindrical-shaped segment of braided polyester filaments that is permanently implanted submucosally in the soft palate, for reducing the incidence of airway obstructions in patients suffering from mild to moderate obstructive sleep apnea. The Pillar device has been associated with a number of adverse side effects, including extrusion, infection, and patient discomfort.
Another implant system sold under the trademark AIRvance™ tongue suspension system by Medtronic ENT, Jacksonville, Fla. employs a titanium screw that is inserted into the posterior aspect of the mandible at the floor of the mouth. A loop of suture is passed through the tongue base and attached to the mandibular bone screw. The AIRvance™ procedure achieves a suspension or hammock of the tongue base making it less likely for the base of the tongue to prolapse during sleep. Due to the high activity of the tongue during wakefulness, the suture component of this device has been shown to act as a “cheese cutter” to the tongue, causing device failure and requiring subsequent removal. Thus, the duration of beneficial effects afforded by the implant is short lived.
Surgical procedures such as UPPP and those mentioned above are painful with extended and uncomfortable healing periods. For example, scar tissue on the soft palate may present a continuing irritant to the patient. Moreover, the procedures are not reversible in the event they happen to induce adverse side effects. As a result, there have been a number of other approaches to treating OSA. For example, devices for electrically stimulating the soft palate to treat snoring and obstructive sleep apnea are disclosed in U.S. Pat. Nos. 5,284,161 and 5,792,067. These devices have had mixed results because they require patient adherence to a regimen of use, subject the patient to discomfort during sleep, and may result in the repeated arousal of the patient. Magnets implanted at various sites in the airway in an attempt to provide forces for manipulating tissue have also been considered for treating sleep apnea. These devices have shown limited success due to implant migration, inability to control the degree of tissue manipulation or treatment, and that the devices only provide temporary results.
In spite of the above efforts, no one device has been used to effectively treat obstructive sleep apnea. Thus, there remains a need for methods and devices that reduce the burden of managing obstructive sleep apnea through minimally invasive approaches that provide long term results, encourage patient compliance, and minimize patient discomfort.